The novel classes of modulated retro-reflective photonic devices described herein may be used for establishing free-space laser communication links, remote data monitoring, IFF (identification of friend or foe), and for enabling multi-port optical communications for optical networks (including relay nodes). Remote data monitoring and secure optical communications with satellites, airborne or ground-based platforms requires that the response to an interrogating light beam needs to be reflected back directly to the source of the light beam itself. One of the main reasons for this is that the pointing and tracking of the beam is eliminated as long as the interrogating light beam illuminates the retro-reflective device.
Systems for communications and identification between two locations using modulators and retroreflectors are known in the art. Issued patents that have addressed the need for laser retro-reflector system for remote data monitoring and IFF includes U.S. Pat. No. 4,731,879 to Sepp et al. entitled, “Remote Data Monitoring System,” wherein a laser and a modulatable retroreflector for the remote interrogation of information from space or targets with a simultaneous IFF. In this system, a liquid crystal modulator is arranged in front of a retroreflector and is modulated by respective information. The system is complex, laser transmitter section comprises laser beam controller means including two-motor driven rotating optical wedge compensators for directing the laser beam, and the transmission frequency is limited to 1-7 kHz only because of the use of liquid crystal modulator. U.S. Pat. No. 4,361,911 to Buser et al. entitled,” Laser Retroreflector System for Identification of Friend or Foe,” also discloses a covert laser retroreflector system to establish IFF capability. The interrogator requires to be a high power laser, and the modulating rertroreflector may be an acousto-optic modulator, a parallel array Pockels cells, or a parallel array of transversely excited Stark Cell in front of a reflecting mirror. The frequency response using acousto-optic (AO) modulator was claimed to reach up to 960 kHz, and to 50 MHz using Pockels Cell modulator for CO2 TEA laser. But CO2 laser will need a cooled HgCdTe detector. Overall the system would require high power, for example for 10.6 μm radiation modulator requires 170-200 watts of RF power. U.S. Pat. No. 6,624,916 to Green et al., entitled, “Signaling System,” describes a free-space point to multipoint signaling system using a retroreflector comprising a telecentric lens for receiving and focusing light from a light source and a reflecting means for said light back. The patent discloses a pixellated modulator forming part of the retroreflecting modulator unit. However, the modulators used are SEED (self-electro-optic effect device), already developed by the American Telephone and Telegraph Company (AT&T). But the range for this type of signaling system is limited to only 150 meters. Some other retroreflector devices for communications and modulators are described in U.S. patents: U.S. Pat. No. 3,989,942 to Waddoups, entitled, “Retro-reflecting laser responser and data modulator,”; U.S. Pat. No. 4,064,434 to Waksberg, entitled, “Retro-reflection communication system,”; U.S. Pat. No. 4,134,008 to de Corlieu et al, entitled, “Light-retroreflecting responser and data modulator arrangement,”; U.S. Pat. No. 4,209,689 to Linford et al, entitled, “Laser secure communications system,”; U.S. Pat. No. 4,887,310 to Meyzonnette, et al, entitled, “Identification system using a laser retro-reflecting and modulating set,”; U.S. Pat. No. 5,459,470 to Wooton et al, entitled “Beam steered laser system,”; U.S. Pat. No. 6,624,916 B1 to Green et al, entitled, “Signaling system,”. U.S. Pat. No. 6,954,302 to Sayyah, et al., describes a conformal retro-modulator optical devise based on an array of multiple quantum well (MQW) devices disposed in a thin array. One of the other prior arts which also includes MQW device is U.S. Pat. No. 6,154,299 to Gilbreath et al., entitled, “Modulating Retroreflector using Multiple Quantum Well Technology,” discloses a system for remote optical communications where the remote station includes a MWQ modulator, and drive circuitry that drives the MQW. The retroreflector reflects the modulated beam to the base station for detection by a receiver. One of the present patent application applicants, Thomas M. Shay has disclosed in U.S. Pat. No. 6,778,779 to Shay et al., entitled, “Full-Duplex Optical Communication Systems,” a method of full-duplex communication using a method of encoding optical information wherein right-hand and left-hand circular polarizations are assigned to optical information. One possible application is for an earth to low orbit optical communications system implementing the full-duplex communication and circular polarization keying modulation format. Besides the above patents, there are a numerous published papers in the open literature where some implementations have attempted to describe modulating retroreflector for communications and other applications. In order to understand the uniqueness and the innovations of the present invention in this patent, a comparison of the various state-of-the-art modulating retroreflector technologies is summarized as follows. Swenson et al. SPIE Proceedings, Vol. 2990, pp. 296-310, 1997, the entirety of which is incorporated herein by reference, describes a Ferroelectric Liquid crystal technology: data rate=1-10 Kbit/s, physical aperture size=15 cm, full field-of-view (FOV)=±44.9°, range demonstrated=30 Km. Olson et al., Appl. Opt. 34 (12), Apr. 20, 1995, the entirety of which is incorporated herein by reference, describes a CO2 laser communication system with modulable retroreflectors with frequency response to 3.5 kHz only with a range of 24 km. But the system requires a cooled detector, laser power of 10-15 W and coherent detection scheme. Luo, et al., IEEE Photonics Technology Letters, Vol. 16, No. 9, pp. 2045-204′7, 2004 discloses an optical micro-electro-mechanical system (MEMS) array: data rate=2.5 Kbit/s, wavelength=1.064 μm, physical aperture size=0.68 cm, range demonstrated=4 m. Bifano et al., http://people.bu.edu/bifano/Retro.html describes MEMS-based modulated retroreflector: data rate=10 KHz, physical aperture=5 mm, power consumption=5 mW, range demonstrated=30 m. MacCannell, et al., Proceedings of the Solid State Diode Laser Technology Review 2002, Albuquerque, N. Mex. May 2002, “Full-Duplex Communication on Single Laser Beam,” described a liquid crystal-based shutter for retromodulation: data rate=20 Kbit/s, wavelength=0.852 μm, physical aperture size=2.26 cm, full FOV=±40.1°, power consumed=120 mW, range demonstrated=30 m. Joseph Ford of the University of California, San Diego described (see T. K. Chan and J. E. Ford, “Deformable MEMS micro mirror array for wavelength and angle insensitive retro-reflecting modulators,” Proceedings of the IEEE LEOS Annual Meeting, Paper ThEE4, Puerto Rico, November 2004.) a MEMS based retromodulator: data rate=100 KHz, FOV=f 68°. Some other papers in the similar areas include: Gunawan et al, “Micromachined corner cube reflectors as a communication link,” Sensors and Actuators A, vol. 46-47, pp. 580-583, 1995; Handerek et al, “Feasibility of retroreflective free-space optical communication using retroreflectors with very wide field of view,” SPIE European Symposium on Optics/Photonics in Security and Defence, Proc. SPIE, vol. 5614, pp. 1-9, 2004. Other papers include the developments of the modulating retroreflectors (MRR) for free space optical communication links at the Naval Research Laboratory (NRL) since 1998. Some of the NRL's disclosures include: Gilbreath et al, “Real time video transfer using multiple quantum well retromodulators,” Proc. SPIE, Vol. 4821, pp. 155-162, 2002; Gilbreath et al, “Modulating retroreflectors for space, tracking, acquisition and ranging using multiple quantum well technology,” Proc. SPIE, Vol. 4821, pp. 494-507, 2002; Goetz et al, “Modulating retroreflector implementation of MIL-STD 1553 protocol with free-space optics,” Proc. II Aerospace Conference Paper No. 1559, 2003; Rabinovich, et al, “Performance of Cat's eye modulating retro-reflectors for free-space optical communications,” Proc. SPIE, Vol. 5550, pp. 104-114, 2004; Wasiczko et al, “Optical communication and navigation for spacecraft docking using modulating retroreflectors,” Proc. SPIE, Vol. 5892, 2005; Murphy et al, “FM-MRR analog audio system,” Proc. SPIE. Vol. 5892, 2005; Rabinovich et al., “Free space optical communications link at 1550 nm using multiple-quantum-well modulating retroreflectors in a marine environment,” Optical Engineering, Vol. 44(5), May 2005: data rate=5 Mbps, FOV=f 60°, physical aperture size=0.63 cm, wavelength=1.55 μm, range demonstrated=2 km; Rabinovich et al, “45 Mbit/s cat's-eye modulating retroreflectors, Optical Engineering, 46(10), October 2007. Also Hemmati et al., Proc. SHE., Vol. 5338, pp. 50-55, 2004, “Retro-Modulator Links with a Mini-Rover,”: describes a retro modulator at the data rate=10 Mbps with a range=2 km. Rabinovich et al., Photonics Technology Letters, November 2003 describes a Cat's Eye multiple quantum well modulating retro-reflector: data rate=50 Mbps, physical aperture=0.5-1 cm, FOV=±30°, wavelength=0.980 μm, power consumed=120 mW. Other recent patent includes the following: U.S. Pat. No. 7,224,905 B2 to Ruggiero, entitled, “Remotely-interrogated high data rate free-space laser communications link,” May 29, 2007 describes a system and method of remotely extracting information from a communications station by interrogation with a low power beam using the property of nonlinear phase conjugation. The only description of the background art which is related to the present patent is the work by Dr. Thomas M. Shay, who is one of the present patent applicants: Shay et al., Proceedings of the SPIE, Vol. 5550, pp. 122-129, 2004, “2.5-Gbps Amplified Retro-Modulator for Free-Space Optical Communications,” describes the first amplified retro-modulated free-space optical communications link: physical aperture=2 cm, pigtailed to a single-mode fiber, wavelength=1.55 μm, FOV=0.004°, power consumed=120 mW.
The prior art using the conventional retroreflector modulation technologies, previously described, have the following drawbacks and limitations. Ferro-electric-liquid crystal (FLC) modulators can achieve modulation rates of only a few kilohertz, which severely limit their bandwidth. Multiple Quantum Well modulated retroreflector can attain a data rate of about 50 Mbps, but are extremely complex devices, limited to relatively small devices and are prohibitively expensive. Neither of those retromodulators can provide a long range (more than a few km) communications link at a high data rate (higher than 50 Mbps). Even the work of Shay et al.'s attempt to couple free-space optics (FSO) signals directly into a “single” single-mode fiber (SMF) to demonstrate 2.5-Gbps data rate was limited to its extremely small FOV of about ±0.004° only, and the demonstration was limited to laboratory experiment without any results for any range (link). None of the FLC, MQW-based and FSO-SMF retromodulation technology has any IFF (identify, friend or foe) capability.